DESCRIPTION: There is considerable evidence that some mercury from "silver fillings" distributes to body tissues, particularly the brain. Occupational exposure to mercury vapor is associated with increases in the prevalence of tremor, peripheral neuropathy, cerebellar dysfunction, and abnormal measures of balance. Occupational exposure also is associated with deficits in neuropsychological tests of memory and visuospatial ability and increased reports of subjective symptoms and disturbed mood. The investigators propose to address the hypothesis that low dose mercury exposure, derived from amalgams in the mouth, may be associated with evidence of neurological dysfunction and neuropsychological deficits. By conducting a cross-sectional study, the investigators will test whether amalgam-derived mercury is adversely associated with tests of neurological function, visuospatial ability, memory and attention/executive function. The study sample will comprise approximately 750-840 Columbia University personnel, ages 30-49 years. Based on preliminary work, it is known that the cohort will have a wide range of visible amalgam surfaces. Measures of exposure will be urinary mercury concentration and the numbers of amalgam surfaces, total and occlusal. The proposed outcome measures tap a wide range of neurological and neuropsychological functions. A variety of tests will assess four domains of neuropsychological function: visuomotor/visuospatial function, memory, attention and executive function, and vocabulary. A self-reported questionnaire of mood and a symptom checklist will also be administered. In addition, the investigators will collect quantitative measures of postural sway. After control for confounding variables, including measures of social desirability and hypochondriasis, the dose-response relationships between exposure and each functional domain will be described. Results from this study will have potential public health applications. Adverse associations, if found, might lead to less use of mercury amalgams. Alternatively, evidence favoring the null hypothesis would allay widespread fears that a variety of health problems may be associated with amalgam exposure.